Hardware Fault Tolerance (HFT), together with Safe Failure Fraction (SFF), determines the Safety Integrity Levels (SIL) of systems
. The HardwareFault Toler ance indicates the number that a system can withstand without failing. The higher the HFT value, the higher the availability. Fail-safe and fault-tolerant systems accordingly have the highest of the three HFT values, 0, 1 and 2.